Conventionally, a gas turbine provided with a so-called active clearance control (AAC) system is known. The AAC system regulates a gap (tip clearance) between a rotor blade and a blade ring of a turbine when starting a gas turbine (see Patent Document 1, for example). In such a gas turbine, the tip clearance is regulated by way of pressurizing a portion of compressed air compressed by a compressor with a pressurizing device and causing the pressurized compressed air to flow into a turbine cooling medium channel via a heating medium supply channel. Furthermore, in this gas turbine, a combustion chamber is cooled by causing the compressed air pressurized with the pressurizing device to flow into a combustion chamber cooling channel via a heating medium branch channel that branches from a heating medium supply channel (see FIG. 10 in Patent Document 1).